From the famous faces who could never really blend in, to the characters who wrecked our hearts with tragic plotlines, these are 17 guest stars we'll never forget.

Best Mad Men guest stars

Rosemarie DeWitt as Midge Daniels

Midge, the beatnik who captured Don's heart in Season 1, was everything Betty was not -- freewheeling, artistic, independent. We'll never forgive Matthew Weiner for reintroducing her in Season 4 with a full-blown heroin addiction, a flailing career and a grotesque husband.

Jay Paulson as Adam Whitman

Seeing characters from Don's true past was always jarring, but few were more shocking than Adam Whitman.

Don's younger half-brother tracked him down, full of excitement at renewing their relationship, but things fell apart when Don cruelly rebuffed him, leading young Adam to commit suicide (the first person to do so in the series).

Image: Mad Men/AMC

Darby Stanchfield as Helen Bishop

Stanchfield played the sharply-dressed divorcee mom of Glen Bishop who was easily able to withstand the withering judgment of Betty and her housewife squad.

She tried to forge a bond with Betty in Season 1, but that went awry because Betty wouldn't give up her strange thirst for Glen's approval.

Image: Mad Men/AMC

Melinda Page Hamilton as Anna Draper

There was something so refreshing about the character of Anna Draper. When she was around, Don was his truest, purest self. She arguably may have even been the only person Don would do anything for -- which made her death even more unfortunate.

Yeardley Smith as Nurse Mary

This might clock as more of a cameo, if you recognize Yeardley Smith's voice. Since 1989, she's been the voice of Lisa Simpson.

Smith made a quick appearance in Season 3, Episode 5, as a hospital nurse where Betty was set to deliver.

Image: Mad Men/AMC

Colin Hanks as Father Gill

...a.k.a. Hot Priest.

Gill entered into Peggy's life in Season 3 as a modern Catholic priest who drinks, smokes and plays guitar. He and Peggy seemed flirtatious -- until Peggy realized she did not give a crap about religion.

Zosia Mamet as Joyce Ramsay

Mamet played Peggy's fast-talking friend who was an assistant photo editor at Life magazine, and one of few lesbians on the show.

She was hip and witty, and always sporting a sharp sports jacket.

Image: Mad Men/AMC

Danny Strong as Danny Siegel

Nepotism got the best of Roger Sterling in Season 4, when (then) wife Jane asked him to find employment for her cousin Danny. Strong (a major player offscreen who's written two Hunger Games films, along with writing and producing Empire) hilariously plays the ineffectual employee with little ad talent.

Image: Mad Men/AMC

Naturi Naughton as Toni Charles

The Playboy bunny girlfriend of Lane Pryce, she was a rare black woman to get a storyline on the series outside of the work office.

Image: Michael Yarish/AMC

Julia Ormond as Marie Calvet

British actress Julia Ormond cut a perfectly-accented turn as Megan Draper's prickly, French-Canadian mother. She was easily one of the shadiest women to ever grace the series, and one of the few who could bring Roger Sterling to his knees.

Image: Mad Men/AMC

Alexis Bledel as Beth Dawes

The doe-eyed seductress had a torrid love affair with Pete Campbell. Things turned tragic, though, when she opted to get electro-shock therapy and forgot who he was.

That twist crushed Campbell, who had fallen madly in love with her. (But fear not, fans -- Bledel and Vincent Kartheiser, the actor who plays Campbell, ended up marrying in real life.)

Neve Campbell as Lee Cabot

Scream queen Neve Campbell made a surprise appearance in Season 7, as a woman Don meets on a red-eye flight. Party of two, please.

Image: Courtesy of AMC

Linda Cardellini as Sylvia Rosen

Nostalgia follows Linda Cardellini everywhere she goes. She of the ill-fated cult series Freaks and Geeks played a woman who had an ill-advised affair with Don, which ended only after Sally discovered them in bed together.

Despite the maddening affair, Cardellini, who is tragically underused by Hollywood, is one of the show's most memorable guests.

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